A rider is necessarily required to wear a helmet when riding a two-wheeled vehicle such as a motorcycle, and the helmet generally has a front opening at a front side of its main body in order to allow a wearer to obtain a front view. Further, the helmet generally has a selectively retractable shield to prevent wind or dust from being introduced through the front opening while the motorcycle moves forwards. Furthermore, a retractable sun visor may be installed within the shield in order to protect the wearer's eyes from direct sunlight in the daytime.
Both end portions of the sun visor are clamped to hinge shafts provided at both lateral sides of the helmet main body, and the clamped sun visor may move forwards and backwards by an operation of a manipulating lever or manipulating grip installed at a top portion of the helmet or one of the both end portions thereof.
However, in case of a sun visor having a manipulating lever installed at one of its both end portions, the other end portion at which the manipulating lever is not installed is configured to passively move. Accordingly, when opening or closing the sun visor, the sun visor may move unstably due to an imbalance in force.
Moreover, even in case of a sun visor having a manipulating lever installed at a top portion of a helmet, it is inconvenient that an opening/closing speed of the sun visor may be too fast or too slow depending on a magnitude of the force applied to the manipulating lever.
Besides, it has been pointed out that the sun visor to be inserted into the helmet main body often collides with the helmet main body, making some collision noise and shortening a life span of the sun visor.